Vacuum insulated glazing (VIG) units comprise a sealed cavity between two glass panes which have been evacuated to a reduced pressure such as 0.001 millibars or less. This low pressure sealed cavity can in turn result in a large pressure asserted on each glass pane towards the sealed cavity. Tempered glass panes can be used in the VIG unit because they have higher strength than regular glass panes, but the disadvantage of tempered glass is the presence of larger surface irregularities compared with regular glass panes. Tempered glass panes generally comprise flatness deviation resulting from the toughening process, such as roller wave distortion which occurs when the soft glass is in contact with rollers in a horizontal toughening process. The distance between two tempered glass panes may therefore vary significantly across the panes.
Pillars, also known as spacers, can be used in VIG units to maintain the sealed cavity thickness and the distance between the glass panes. The pillars can comprise a high compressive strength material that is capable of withstanding the pressures exerted on them from outside the VIG unit by the atmospheric pressure on the external side of the glass panes such that the sealed cavity is maintained. Not only is it desirable to have pillars which comprise a high compressive strength, but also pillars which can allow a certain degree of shear as the glass panes move relative to each other in a direction parallel to the extent of the glass panes, which for example can occur due to thermal expansion and/or wind pressure that can affect the installed VIG unit. Similarly, it is also of advantage having pillars which can relieve any stresses occurring in the glass panes due e.g. to an impact force applied to the glass panes in a direction perpendicular to the glass surface.
Additionally it is desirable that the insulating properties and the transparency of the VIG unit are not significantly affected by the pillars.
Therefore, there remains a continuing need for pillars that can be used between glass panes of a VIG unit, and in particular to pillars that can accommodate for variations in spacing between the glass panes due to glass surface irregularities, thermal transitions, and compressive forces.
EP patent application no. EP 1 018 493 A1 describes a number of different pillars for a vacuum insulated glass panel, including pillars of fixed and variable height. E.g., a pillar is described having two planar contacting faces abutting the glass panes and comprising an elastic member in between, in the form of, e.g., a spring, an open structure, or an elastically deformable material. The pillars are described as being adapted to account for displacements of the panes along and perpendicular to the glass surfaces, such as tempered glass surfaces.
U.S. Pat. No. 6,479,112 describes a glass panel having two glass panes, such as tempered glass panes, separated at pre-determined distance using pillars having a contact surface facing the inner surface of one of the glass panes which comprises protrusion. The pillars are made to a pre-determined height using hard materials such as metal or solder glass. In one embodiment, the pillars may alternatively be made of rubber, such as synthetic resin rubber, allowing the pillar to be flexible and absorb any flexural movement of the panes.
U.S. Pat. No. 6,210,763 describes a pillar, e.g. of cylindrical shape and made of aluminium alloy, capable of maintaining a predetermined distance between two glass panes, such as tempered glass panes, and at the same time be able to relieve stress due to impact through plastic deformation in the pillar.
European patent application EP 3 210 944 A1 discloses a vacuum glass panel having two glass panes, where in order to compensate for surface undulation of the panes, pillars with corresponding heights are arranged on corresponding positions between the layers of plate, and the heights of the pillars match with the spacing between the glass panes at corresponding positions in the vacuum glass panel, so that each pillar can be clamped by the upper and the lower pane and effectively plays a supporting role.